Field of the Invention
The present invention relates to tooling for fabricating a foundry core for making a cooling circuit in a turbine engine blade.
Description of the Related Art
A turbine engine blade, and in particular a blade for a turbine wheel of a turbine engine, includes a cooling circuit that is fed with air via orifices formed in the blade root, these orifices opening out into internal cavities of the blade that communicate with a bathtub at the tip of the airfoil of the blade. The bathtub is formed by a recess at the tip of the blade, being separated from internal cavities in the blade by a bathtub bottom wall, and it is in fluid flow communication with the internal cavities via orifices passing through said bottom wall. In operation, air penetrates into the orifices in the blade root, flows along the internal cavities in the blade, and is then expelled, in part into the bathtub via the above-mentioned orifices, and in part into the annular passage through the turbine via air outlet orifices in the airfoil of the blade.
The cooling circuit of a blade of this type includes in particular the bathtub, the internal cavities in the blade, and the orifices in the bathtub bottom wall that provide fluid flow communication between the bathtub and the internal cavities.
This cooling circuit is complex in shape and it is generally obtained by means of a foundry core that is inserted in a mold into which a molten metal is cast in order to make the blade.
Documents EP-A1-1 661 642, EP-B1-1 754 555 and EP-A1-1 980 343 describe cores of this type.
The core is generally made from a paste comprising ceramic fillers and a polymer-based binder, which paste is injected into a mold of tooling and is then heated in order to solidify the core.
In the prior art, the mold of the tooling includes imprints for a first portion of the core that is to form the bathtub of the blade, and for one or more other portions imprint that are to form one or more respective internal cavities of the blade.
The mold includes a wall separating the first portion of the imprint from the or the other portions of the core, this wall serving to define a space in the core between its first portion and its other portions. During fabrication of the blade, molten metal penetrates into this space in the core in order to form of the above-mentioned bathtub bottom wall of the blade.
As explained above, this bathtub bottom wall is pierced by orifices. These orifices are obtained in casting by means of ceramic rods that are positioned in the mold, prior to fabricating the core, and that form integral portions of the core after it has been fabricated.
Each ceramic rod generally connects the first portion of the core to one of the above-mentioned other portions (EP-B1-1 754 555).
In the prior art, the mold for fabricating the core includes means for bearing against and/or embedding end portions of each rod. One of those means is formed on the above-mentioned wall of the mold, and the other means is formed on another portion of the mold, that is opposite from the above-mentioned wall relative to the imprint for the first portion of the core. Each rod thus passes through the imprint of the first portion of the mold.
In particular, the diameter of the orifices in the bathtub bottom wall is a function of the diameter of the ceramic rods of the core. To reduce the diameter of these orifices, it is possible to reduce the diameter of the rods. Nevertheless, it has been found that rods of small diameter (e.g. of about 0.6 millimeters (mm)) are relatively fragile and frequently break while the paste is being injected into the mold, thereby causing the core to be scrapped.